NEIM1031: in-line noise eliminator module from BHI

Hi all,

Always keeping in mind to improve the reception on the noisy low bands, I wanted to acquire some external DSP treatments. The internal DSP of the FT920 is not that good (in my mind, or at least, not good enough ...), so I started to search on Internet which one would be convenient here.

My constraint was that I wanted
- Something effective (for which I wanted to hear its effectiveness before purchasing)
- Something simple (Not 100000 knobs with hidden menu adjustments)
- Something I could plug my headphones on (I'm 100% headphones user)
- Something I could put ON/OFF easily, and with easily variable filtering levels.

Of course, there are the famous Timewave products, MFJ784b etc, but from spec point of view, their "random noise" reduction is up to 20dB only (roughly 3 S-meter points)..And my noise on the low bands is closer to S5-S6....

After a quite long survey, I found the BHI company to deliver many products dealing with audio treatments, including the in-line module NEIM1031, which is specified for, 35dB of random noise reduction. That's perfect !


This unit is very easy to install : A 3.5mm male to 3.5mm male audio cable is necessary to connect the transceier adjustable audio output to the audio IN input of the unit, a 3.5mm output socket to connect the headphones, and a simple power supply on the side.

- Firing the unit
I strictly respected the manual. The most difficult was to adjust the input/output level knobs so that
- the green LED lights enough
- the audio level remains identical by switching ON/OFF the unit.

Once this was done (it took me 15seconds or so !), then I just played with the noise reduction levels (from 0 to 7) and obsere what it was doing. Note that noise elmination takes effect after a bried delay after enabling the DSP (said this is normal in the manual)

Results are already impressive, although I just put this unit in service yesterday. But I wanted to test it in the real field (low bands) as soon as possible.
40m evening time in Europe, noisy as usually:
1st test:
A XU7 station is spotted, which is could very barely read on the vertical alone (almost buried in the noise)
NEIM1031 ON : Level 0 --> almost no improvment
Level 1 and  2: Progressive improvment, but still hard to copy
Level 3: It is becoming easier !!!!!!
Level 4: Small water sound in the background appears, but I could live with it. 
Level 5 and above: Background noise progressively hears like a watery sound, sometimes covering the signal of the XU7 station.
--> First test conclusion : Level 4 enabled me to have a nice reading of the station, which was, remember, very barely readable before.

2nd test: There was a 9A station, 5/9 here, with some background noise at S5-S6. Quite easy reading, but he was not speaking, this noise is quite terrible to hear.
I directly go to level 6 and 7 to see: Wtatery sound still here.
Level 5: Perfect, almost no more background noise, and a real armchair copy of the 9A.

3rd test: FM1FV on 80m this morning
Slightly above the noise level (signal at S6, noise at S5), but still tiring to listen too.
Level 1, 2 and 3, improvment, but some noise still there (less and less)
Level 4: Perfect (small watery sound was insignificant compared to the wanted signal)
Level 5 and above: Watery sound increasing.

Conclusion (my observations)

The higher the S/N is originally, the higher the DSP level can ben and the easier the reading will be..
If the signal is slightly above your noise level, middle DSP level will enable you to have a full reading of it (it would have been longer/tougher/almost impossible without filtering)
If the signal is at your noise level, small amount of DSP can be used to make it more easily readable, and trade-off has to be found so that the background "watery" sound is not too annoying.

If you basically do not hear the station originally, I still didn't find anything magic in this box. That might be possible to read it, depending on the noise type and the level filterings, but I doubt this can be easily reproducible.

In any case, this is a very nice improvment for my reception on the low bands !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

To continue:
- Preliminary results are VERY VERY VERY encouraging.

I'll play today
- on the high bands, even if they are less noisy.
- with my homemade HF preselector/preamplifier --> 20dB gain level and 20-25dB noise reduction should normally do a good job, HI !
- with the settings of my FT-920 DSP: 2 serial DSP's, that should also improve the RX !!!!!

If you want more details on this unit (as well as hearing the effectiveness of this filtering), you can go there:
Main site: http://www.bhinstrumentation.co.uk/
Sound examples (I made my choice thanks to this!) : http://www.radio.bhinstrumentation.co.uk/html/sound_file_demonstration.html

The NEIM1031 datsheet, manual, etc : http://www.bhinstrumentation.co.uk/html/neim1031_in-line_module.html

My review on eham: http://www.eham.net/reviews/review/77601

73
Ronan, F8AFC